The invention relates to a phased array antenna system, comprising at least two phased array antenna faces, both provided with an array of radiating elements, an array of T/R modules connected to the array of radiating elements, a summing network for summing output signals of the array of T/R modules and a control unit for generating control signals for the individual antenna faces.
Antenna systems of this type are well-known in the art and are for instance used on board naval ships for a substantial number of tasks which, until recently, required the availability of several separate fire-control and surveillance radar systems.
With multi-face phased array antenna systems it is preferably assumed that the various antenna faces are capable of operating independently. In this respect, a more specific assumption is that transmission by one antenna face and reception by another antenna face may coincide, or worded differently, that the insulation between the various faces is satisfactory. Broadly speaking, this is true: it is possible to design the antenna faces such that the side lobe level is kept to a minimum, thus providing a sufficient insulation for any combination of beam directions.
The installation of the phased array antenna system on board a ship may alter the situation. If a large object, a ferry-boat for instance, is irradiated by two different antenna faces simultaneously, which is possible because beams generated by two adjacent antenna faces will usually overlap to a slight extent, the infeasibility of coincident transmission and reception can be readily ascertained. This problem may also occur for less powerful reflectors. Initially, this problem can be easily solved by scheduling the transmissions for adjacent antenna faces in such a manner that the beams are not parallel or not substantially parallel and by stipulating, in case of transmissions for adjacent antenna faces, a predetermined frequency difference. Notwithstanding these measures, the antenna face side lobes in combination with a powerful reflector in the vicinity of the antenna system are still found to cause crosstalk from one antenna face to another.